1. Field of the Invention
The present invention relates to a sheet finisher for an image forming apparatus, and more specifically to the sheet finisher that detects movement of an arm member contacting recording media output to a tray of the sheet finisher.
2. Discussion of the Related Art
Conventionally, a stack of recording media folded in a predetermined manner is discharged to a tray or sheet loading system of a sheet finishing apparatus. For example, a typical sheet loading system includes a discharge roller that discharges a center-folded and stapled stack of sheets (sometimes referred to as a sheet stack). The sheet loading system includes a pressure arm that presses a surface of the sheet stack received on the tray, and a detecting member that detects the presence and absence of the sheet stack on the tray. The sheet loading system is generally sized to receive several dozen sheets.
In order to prevent the output of a larger number of sheet stacks than can be received by the tray, it is known to control the output to the sheet stacks to the tray based on an output from the detecting member. However, the detecting member is able only to detect the receipt of the first sheet stack on the tray. Therefore, after the detecting member detects the first sheet stack, a separate counter counts the number of sheet stacks output to the tray. When the counter counts a number of sheet stacks equal to a predetermined number, a signal indicating a tray full condition prevents further sheet stacks from being output to the tray. After a user removes the sheet stacks loaded on the tray, the detecting member detects the absence of any sheet stacks on the tray, and the counter is reset.
FIG. 1 is a side view of a known sheet finishing apparatus including a sheet loading system. As shown in the figure, the sheet finishing apparatus includes lower outlet rollers 1083, a lower tray 1203, a pressure arm 1501, a rotation fulcrum 1501a, and a sensor 1401. Center-bound sheet stacks are received on the lower tray 1203.
Specifically, sheet stacks of recording media folded in a predetermined manner are output by the lower outlet rollers 1083 to the lower tray 1203. The rotation fulcrum 1501a of the pressure arm 1501 is disposed adjacent the lower outlet rollers 1083. The pressure arm 1501 presses the surface of the sheet stacks. The sensor 1401 detects the presence or absence of the first sheet stack in the lower tray 1203. After the sensor 1401 detects the first sheet stack, a separate counter counts the number of sheet stacks output to the lower tray 1203. When the counter counts a number of sheet stacks equal to a predetermined number, a signal indicating a tray full condition prevents further sheet stacks from being output to the lower tray 1203.
A memory that stores the counted number of sheet stacks may be erased, however, when the power to the image forming apparatus including the sheet finishing apparatus is turned off, or when the image forming apparatus enters a power saving mode. Because the sheet finishing apparatus cannot determine the number of sheet stacks on the lower tray 1203 after the memory is erased, the image forming apparatus indicates the tray full condition and requires that all sheet stacks on the lower tray 1203 be removed before output of additional sheet stacks to the lower tray 1203 is permitted. Emptying the lower tray 1203 is required even if only one sheet stack is on the lower tray 1203, because the number of sheet stacks on the lower tray 1203 cannot be determined.
When the image forming apparatus is not located near the user, it is inconvenient for the user to make multiple required trips to remove all of the sheet stacks from the lower tray 1203.